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Solder Joint Oxidation Scale
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Solder Joint Oxidation Scale

by DJDevon3 on Sat Aug 17, 2019 4:14 pm

I'm taking apart one of my previous projects and notice most of the solder joints have a lot of oxidation scale buildup on the joints. Instead of looking like a fresh solder joint after 3 months it looks like solder joints I've seen in equipment after 30 years. I'm using 60/40 Kester and a basic Weller iron. I also generally use Oatey #30130 water soluble paste flux. I don't clean the flux off with a cleaner just a towel most times. My tip is generally very well maintained and sometimes I use tip tinner (thermaltronics tmt-tc-2). I feel like I'm doing something obviously wrong in my soldering process to get that much scale. Any tips appreciated.

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Re: Solder Joint Oxidation Scale

by adafruit_support_bill on Sat Aug 17, 2019 4:39 pm

Are you sure it is oxidation and not just flux residue? Does it come off with some water or alcohol? You may need to scrub a bit with an old toothbrush.

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Re: Solder Joint Oxidation Scale

by DJDevon3 on Mon Aug 19, 2019 9:26 pm

After going back through some of my old soldering projects I found that the solid flux gel/paste was still in little areas of the board. I didn't clean up at all. The flux I'm using doesn't just evaporate, I honestly thought it would. It leaves a nasty coating which can actually aid oxidation. Watched some youtube videos about procedures and I've been doing it all wrong. Got some 99% IPA and some little brushes.

It's little things like this I took for granted in my projects. A video on good hand soldering techniques when using Adafruit modules would be a nice addition for newbies. I've watched Digikey videos on it but no one mentions good clean up procedures to ensure the joints stay shiny and last. If they do exist perhaps I missed finding them?

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Re: Solder Joint Oxidation Scale

by adafruit_support_bill on Tue Aug 20, 2019 5:57 am

We have a soldering tutorial with video here: https://learn.adafruit.com/adafruit-gui ... ring/tools
But it does not address cleanup after soldering.

I use flux-core Kester (rosin flux) for most of my work and have not found residue to be a problem. Sometimes when working with difficult things (e.g. old oxidized stranded wire) I'll need to use some additional liquid flux. In those cases usually clean up with some >90% IPA.

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Re: Solder Joint Oxidation Scale

by zener on Tue Aug 20, 2019 12:04 pm

That Oatey product is for plumbing connections not electronics. As was said a rosin core solder is great for most applications, and it actually does not have to be cleaned off, although many people do for appearance. There are also water wash flux core solders and so-called "no-clean" and those definitely leave a residue but you don't have to clean it. And, although you did not mention it, I would stay away from lead free solder, at least until you develop some strong soldering skills. Personally I don't use it and I don't know anyone who does, for general hobby soldering.

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Re: Solder Joint Oxidation Scale

by adafruit_support_mike on Wed Aug 21, 2019 3:09 am

zener wrote:That Oatey product is for plumbing connections not electronics.

That's a very important point.

Plumbing flux contains zinc chloride and ammonium chloride, both of which decompose into hydrochloric acid at soldering temperatures. HCl is great at dissolving oxide layers, but remains a concentrated acid at room temperature. If you leave it on a PCB it will attack the components and copper traces.

HCl doesn't really evaporate, but is extremely soluble in water. It dissolves into humidity in the air, then travels through the air to anything near the original joint. You end up with a monolayer of strong acid on all exposed surfaces.

To make things even worse, HCl on metal turns into a regenerating corrosive agent:

1) Two molecules of HCl will give their chlorine to a metal atom, producing H2 and metal-Cl2.
2) An excess of metal (like the bulk of any object made of metal) will split metal-Cl2 into two molecules of metal-Cl.
3) An excess of oxygen (like a surface exposed to the air) strips chlorine away from metal-Cl, producing metal-oxide and free chlorine.
4) Metal-Cl bonds with free chlorine to make metal-Cl2 again.

The whole process works even better in the presence of water.. like the film of humidity adsorbed to the surface of metal in any normal atmosphere.

Trying to clean a chloride-tainted workspace is a huge pain in the neck, so avoid it if you can.

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Re: Solder Joint Oxidation Scale

by DJDevon3 on Wed Aug 21, 2019 3:50 pm

decompose into hydrochloric acid at soldering temperatures.
Sounds like a ticking time bomb. Well that's great. All of my previous projects are doomed to corrode.

Ahhh yes I originally got the Oatey for a brazing project for compressed air lines in the garage. Didn't even think about that. Flux is flux?

I live in a tropically humid environment and my garage can reach up to 120F during summer at 100% humidity perhaps speeding up the process.

Pretty sure the 60/40 Kester is rosin core so I'm adding 2 different kinds of flux whenever I solder? The one inside the solder and the plumbing Oatey flux? Disaster waiting to happen.

Here's a link to the Kester 60\40 rosin core. https://www.amazon.com/gp/product/B00068IJPO
and the Flux https://www.amazon.com/gp/product/B000V88WJW (plumbing flux durrrrrrr)
and the tip tinner https://www.amazon.com/gp/product/B00NS4J6BY

Think this mystery is solved. Thank you everyone for your advice.

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Re: Solder Joint Oxidation Scale

by zener on Wed Aug 21, 2019 4:42 pm

Tip tinner is good stuff. I never used that brand but I assume they are all similar.

That solder looks good. I prefer 63/37:

https://www.amazon.com/Kester-24-6337-0027-Solder-Alloy-Diameter/dp/B0149K4JTY/ref=sr_1_4?keywords=KESTER+SOLDER+63%2F37+Stand%2C+0.031%22&qid=1566419715&s=industrial&sr=1-4

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Re: Solder Joint Oxidation Scale

by DJDevon3 on Wed Aug 21, 2019 5:55 pm

I'm fine working with the 60/40 Kester it's good stuff. It was the flux that was the problem.

Added the Chip Quik no clean flux pen. I don't solder a lot so this seems the right amount for my needs.
https://www.adafruit.com/product/3468

Even though technically with rosin core I shouldn't need flux I found using it still helped suck the solder onto the pad much easier. Even though it was the wrong kind of flux it was still very helpful. Had no clue the plumbing flux I was using would be so corrosive. Sometimes it helps to make mistakes public so others can learn what not to do. Sharing your mistakes can sometimes be more helpful than sharing your successes.

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Re: Solder Joint Oxidation Scale

by adafruit_support_mike on Thu Aug 22, 2019 2:02 am

Talking about mistakes and things that went wrong is a big part of Maker culture.. "something went wrong" is the natural state of any project, and it's rare to have anything work the first time you try it.

One of the quotes that show up at the bottom of every page is from Neils Bohr: "An expert is someone who has made all the mistakes which can be made, in a narrow field." It looks ironic at first glance, but being able to recognize and correct a wide range of mistakes is an incredibly valuable skill.

We live in a world that only shows the final product, not the pile of failures it took to get there:

https://www.youtube.com/watch?v=rDjrOaoHz9s

layered on top of a dozen years of "neatness counts" and "you only get to take the test once" indoctrination as we grow up. The natural and completely logical result is that people who are interested in beoming Makers start with a sense of inferiority and a big dose of option paralysis, which is 100% firmly-tamped bovine excreta.

The farther you go up the chain of expertise and renown in the Maker community, the more determination you'll find to not just admit mistakes but to spotlight and broadcast them. Every time Adam Savage grins at the camera on YouTube and says, "I just screwed up," he does more good for beginning Makers than a hundred "look at my final product" presentations.

The truth of Making is that everything is a test, you may or may not have the information you need to succeed, but you get as many do-overs as you have the endurance to take. We need to get that information out to the rest of the world.

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